3,233,404 research outputs found
Massive Fields of Arbitrary Integer Spin in Symmetrical Einstein Space
We study the propagation of gauge fields with arbitrary integer spins in the
symmetrical Einstein space of any dimensionality. We reduce the problem of
obtaining a gauge-invariant Lagrangian of integer spin fields in such
background to an purely algebraic problem of finding a set of operators with
certain features using the representation of high-spin fields in the form of
some vectors of pseudo-Hilbert space. We consider such construction in the
linear order in the Riemann tensor and scalar curvature and also present an
explicit form of interaction Lagrangians and gauge transformations for massive
particles with spins 1 and 2 in terms of symmetrical tensor fields.Comment: 15 pages, latex, no figures,minor change
Isotope effects in high-Tc cuprate superconductors: Ultimate proof for bipolaron theory of superconductivity
Developing a theory of high-temperature superconductivity in copper oxides is
one of the outstanding problems in physics. Twenty-five years after its
discovery, no consensus on the microscopic theory has been reached despite
tremendous theoretical and experimental efforts. Attempts to understand this
problem are hindered by the subtle interplay among a few mechanisms and the
presence of several nearly degenerate and competing phases in these systems.
Here we provide unified parameter-free explanation of the observed
oxygen-isotope effects on the critical temperature, the magnetic-field
penetration depth, and on the normal-state pseudogap for underdoped cuprate
superconductors within the framework of the bipolaron theory compatible with
the strong Coulomb and Froehlich interactions, and with many other independent
observations in these highly polarizable doped insulators. Remarkably, we also
quantitatively explain measured critical temperatures and magnitudes of the
magnetic-field penetration depth. The present work thus represents an ultimate
proof of the bipolaron theory of high-temperature superconductivity, which
takes into account essential Coulomb and electron-phonon interactions.Comment: 8 pages, 2 figure
Reversibility conditions for quantum channels and their applications
A necessary condition for reversibility (sufficiency) of a quantum channel
with respect to complete families of states with bounded rank is obtained. A
full description (up to isometrical equivalence) of all quantum channels
reversible with respect to orthogonal and nonorthogonal complete families of
pure states is given. Some applications in quantum information theory are
considered.
The main results can be formulated in terms of the operator algebras theory
(as conditions for reversibility of channels between algebras of all bounded
operators).Comment: 28 pages, this version contains strengthened results of the previous
one and of arXiv:1106.3297; to appear in Sbornik: Mathematics, 204:7 (2013
A Field Theory for Fermionic Ladder with Generic Intrachain Interactions
An effective low energy field theory is developed for a system of two chains.
The main novelty of the approach is that it allows to treat generic intrachain
repulsive interactions of arbitrary strength. The chains are coupled by a
direct tunneling and four-fermion interactions. At low energies the individual
chains are described as Luttinger liquids with an arbitrary ratio of spin
and charge velocities. A judicious choice of the basis for the decoupled
chains greatly simplifies the description and allows one to separate high and
low energy degrees of freedom. In a direct analogy to the bulk cuprates the
resulting effective field theory distinguishes between three qualitatively
different regimes: (i) small doping (), (ii) optimal doping () and (iii) large doping (). I discuss the excitation
spectrum and derive expressions for the electron spectral function which turns
out to be highly incoherent. The degree of incoherence increases when one
considers an array of ladders (stripe phase).Comment: 32 pages, 4 figures. A section explaining adiabatic approximation is
modified. Typos correcte
Comparative study of selected indoor concentration from selective laser sintering process using virgin and recycled polyamide nylon (pa12)
Additive manufacturing (AM) stands out as one of the promising technologies that
have huge potential towards manufacturing industry. The study on additive manufacturing
impact on the environment and occupational exposure are attracting growing attention recently.
However, most of the researcher focus on desktop and fused deposition modelling type and less
attention given to the industrial type of AM. Usually, during the selective laser sintering process,
recycle powder will be used again to reduce cost and waste. This article compares the PM 2.5,
carbon dioxide (CO2) and total volatile organic compound (TVOC) concentration between virgin
and recycles powder using polyamide-nylon (PA12) towards indoor concentration. Four phases
of sampling involve during air sampling accordingly to the Industry Code of Practice on Indoor
Air Quality 2010 by DOSH Malaysia. It was found that PM 2.5 and CO2
concentration are mainly
generated during the pre-printing process. The recycle powder tended to appear higher compared
to virgin powder in terms of PM 2.5, and CO2. The peak value of PM 2.5 is 1452 μg/m3 and CO2
is 1218 ppm are obtained during the pre-printing process during 8 hours of sampling. TVOC
concentration from recycling powder is slightly higher during the post- printing phase where
confirm the influence of the powder cake and PA12 temperature from the printing process. In
summary, this work proves that elective laser sintering (SLS) machine operators are exposed to
a significant amount of exposure during the SLS printing process. Mitigation strategies and
personal protective equipment are suggested to reduce occupational exposure
FDM preparation of bio-compatible UHMWPE polymer for artificial implant
Due to its properties of high wear, creep resistance, high stiffness and strength, Ultra-High Molecular Weight Polyethylene (UHMWPE) was developed to eliminate most metallic wear in artificial implant, which conventionally found in stainless steel, Cobalt Chromium (Co-Cr) and Titanium (Ti) alloys. UHMWPE has an ultra-high viscosity that renders continuous melt-state processes including one of the additive manufacturing processes, Fused Deposition Modeling (FDM) ineffective for making UHMWPE implant. Attempt to overcome this problem and adapting this material to FDM is by blending UHMWPE with other polyethylene including High Density Polyethylene (HDPE) and Polyethylene-Glycol (PEG) which provide adequate mechanical properties for biomedical application along with the improvement in extrudability. It was demonstrated that the inclusion of 60% HDPE fraction has improved the flowability of UHMWPE in MFI test and showing adequate thermal stability in TGA
Solution of Linear Programming Problems using a Neural Network with Non-Linear Feedback
This paper presents a recurrent neural circuit for solving linear programming problems. The objective is to minimize a linear cost function subject to linear constraints. The proposed circuit employs non-linear feedback, in the form of unipolar comparators, to introduce transcendental terms in the energy function ensuring fast convergence to the solution. The proof of validity of the energy function is also provided. The hardware complexity of the proposed circuit compares favorably with other proposed circuits for the same task. PSPICE simulation results are presented for a chosen optimization problem and are found to agree with the algebraic solution. Hardware test results for a 2–variable problem further serve to strengthen the proposed theory
The fastest way to circle a black hole
Black-hole spacetimes with a "photonsphere", a hypersurface on which massless
particles can orbit the black hole on circular null geodesics, are studied. We
prove that among all possible trajectories (both geodesic and non-geodesic)
which circle the central black hole, the null circular geodesic is
characterized by the {\it shortest} possible orbital period as measured by
asymptotic observers. Thus, null circular geodesics provide the fastest way to
circle black holes. In addition, we conjecture the existence of a universal
lower bound for orbital periods around compact objects (as measured by
flat-space asymptotic observers): , where is the
mass of the central object. This bound is saturated by the null circular
geodesic of the maximally rotating Kerr black hole.Comment: 5 page
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